EFR32FG 2.4 GHz / 490 MHz Dual Band
19.5 dBm Radio Board
BRD4251A Reference Manual
The EFR32FG family of Wireless SoCs deliver a high performance, low energy wireless solution integrated into a small form
factor package.
RADIO BOARD FEATURES
• Wireless SoC:
EFR32FG1P133F256GM48
By combining high performance sub-GHz RF and 2.4 GHz RF transceivers with an energy efficient 32-bit MCU, the family provides designers the ultimate in flexibility with a
family of pin-compatible devices that scale from 128/256 kB of flash and 16/32 kB of
RAM. The ultra-low power operating modes and fast wake-up times of the Silicon Labs
energy friendly 32-bit MCUs, combined with the low transmit and receive power consumption of the sub-GHz and 2.4 GHz radios result in a solution optimized for battery
powered applications.
• CPU core: ARM Cortex-M4 with FPU
To develop and/or evaluate the EFR32 Flex Gecko the BRD4251A Radio Board can be
connected to the Wireless Starter Kit Mainboard to get access to display, buttons and
additional features from Expansion Boards.
• Transmit power: 19.5 dBm
• Flash memory: 256 kB
• RAM: 32 kB
• Dual band transceiver integrated in the
Wireless SoC: EFR32
• Operation frequencies: 2.4 GHz
+ 490 MHz
• 2.4 GHz: Integrated PCB antenna.
• 490 MHz: Single SMA connector both for
transmit and receive
• Crystals for LFXO and HFXO: 32.768 kHz
and 38.4 MHz.
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Introduction
1. Introduction
The EFR32 Flex Gecko Radio Boards provide a development platform (together with the Wireless Starter Kit Mainboard) for the Silicon
Labs EFR32 Flex Gecko Wireless System on Chips and serve as reference designs for the matching networks of the RF interfaces.
The BRD4251A Radio Board supports dual-band operation with its integrated sub-GHz ISM band and 2.4 GHz band transceivers. The
sub-GHz section is designed to the operate in the AMR 470-510 MHz band with an external whip antenna, the 2.4 GHz section is designed to operate at the 2400-2483.5 MHz band with the on-board printed antenna. The matching networks are optimized to 19.5 dBm
output power.
To develop and/or evaluate the EFR32 Flex Gecko the BRD4251A Radio Board can be connected to the Wireless Starter Kit Mainboard
to get access to display, buttons and additional features from Expansion Boards and also to evaluate the performance of the RF interfaces.
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Radio Board Connector
2. Radio Board Connector
2.1 Introduction
The board-to-board connector scheme allows access to all EFR32FG1 GPIO pins as well as the RESETn signal. For more information
on the functions of the available pin functions, we refer you to the EFR32FG1 Datasheet.
2.2 Radio Board Connector Pin Associations
The figure below shows the pin mapping on the connector to the radio pins and their function on the Wireless Starter Kit Mainboard.
P200
Upper Row
3v3
NC / P36
NC / P38
NC / P40
NC / P42
NC / P44
DEBUG.TMS_SWDIO / PF1 / F0
DEBUG.TDO_SWO / PF2 / F2
DEBUG.RESET / RADIO_#RESET / F4
VCOM.TX_MOSI / PA0 / F6
VCOM.#CTS_SCLK / PA2 / F8
UIF_LED0 / PF4 / F10
UIF_BUTTON0 / PF6 / F12
DISP_ENABLE / PD15 / F14
DISP_SI / PC6 / F16
DISP_EXTCOMIN / PD13 / F18
PTI.DATA / PB12 / F20
USB_VBUS
5V
Board ID SCL
P201
Lower Row
GND
GND
P37 / PD15 / SENSOR_ENABLE VCOM.#CTS_SCLK / PA2 / P0
VCOM.#RTS_#CS / PA3 / P2
P39 / NC
UIF_BUTTON0 / PF6 / P4
P41 / NC
UIF_BUTTON1 / PF7 / P6
P43 / NC
UIF_LED0 / PF4 / P8
P45 / NC
DEBUG.TDI / PF3 / P10
F1 / PF0 / DEBUG.TCK_SWCLK
PC10 / P12
F3 / PF3 / DEBUG.TDI
PA4 / P14
F5 / PA5 / VCOM_ENABLE
VCOM_ENABLE / PA5 / P16
F7 / PA1 / VCOM.RX_MISO
PTI.CLK / PB11 / P18
F9 / PA3 / VCOM.#RTS_#CS
PTI.DATA / PB12 / P20
F11 / PF5 / UIF_LED1
PTI.SYNC / PB13 / P22
F13 / PF7 / UIF_BUTTON1
DEBUG.TMS_SWCLK / PF0 / P24
F15 / PC8 / DISP_SCLK
DEBUG.TMS_SWDIO / PF1 / P26
F17 / PD14 / DISP_SCS
DEBUG.TDO_SWO / PF2 / P28
F19 / PB13 / PTI.SYNC
NC / P30
F21 / PB11 / PTI.CLK
UIF_LED1 / PF5 / P32
USB_VREG
NC / P34
GND
GND
Board ID SDA
VMCU_IN
P1 / PC6 / DISP_SI
P3 / PC7
P5 / PC8 / DISP_SCLK
P7 / PC9
P9 / PA0 / VCOM.TX_MOSI
P11 / PA1 /VCOM.RX_MISO
P13 / PC11
P15 / NC
P17 / NC
P19 / NC
P21 / NC
P23 / NC
P25 / NC
P27 / NC
P29 / NC
P31 / PD13 / DISP_EXTCOMIN
P33 / PD14 / DISP_SCS
P35 / PD15 / DISP_ENABLE
VRF_IN
Figure 2.1. BRD4251A Radio Board Connector Pin Mapping
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Radio Board Block Summary
3. Radio Board Block Summary
3.1 Introduction
This section gives a short introduction to the blocks of the BRD4251A Radio Board.
3.2 Radio Board Block Diagram
The block diagram of the BRD4251A Radio Board is shown in the figure below.
I2C
UFL
Connector
2.4 GHz RF
GPIO
UART
2.4 GHz RF
Matching
Network &
Path
Selection
2.4 GHz RF
SubGHz RF
Matching
Network &
DC Bias
SubGHz RF
Debug
AEM
EFR32
EFR32
Wireless SoC
Packet Trace
SMA
Connector
SPI
SPI
I2C
Radio
Board
Connectors
Inverted-F
PCB
Antenna
24AA0024
8 Mbit
MX25R
Serial EEPROM
Serial Flash
8k
.76
32
LF
Crystal
.4M
38
HF
Crystal
Figure 3.1. BRD4251A Block Diagram
3.3 Radio Board Block Description
3.3.1 Wireless MCU
The BRD4251A EFR32 Flex Gecko Radio Board incorporates an EFR32FG1P133F256GM48 Wireless System on Chip featuring 32-bit
Cortex-M4 with FPU core, 256 kB of flash memory 32 kB of RAM, an integrated 2.4 GHz band and an integrated sub-GHz ISM band
transceiver with output power up to 19.5 dBm. For additional information on the EFR32FG1P133F256GM48, refer to the EFR32FG1
Data Sheet.
3.3.2 LF Crystal Oscillator (LFXO)
The BRD4251A Radio Board has a 32.768 kHz crystal mounted.
3.3.3 HF Crystal Oscillator (HFXO)
The BRD4251A Radio Board has a 38.4 MHz crystal mounted.
3.3.4 Matching Network for Sub-GHz
The BRD4251A Radio Board incorporates a sub-GHz matching network which connects both the sub-GHz TX and RX pins of the
EFR32FG1 to the one SMA connector to be able to transmit and receive with one antenna. The component values were optimized for
the 490 MHz band RF performace and current consumption with 19.5 dBm output power.
For detailed description of the matching network see Chapter 4.2.1 Description of the Sub-GHz RF Matching.
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Radio Board Block Summary
3.3.5 Matching Network for 2.4 GHz
The BRD4251A Radio Board incorporates a 2.4 GHz matching network which connects the 2.4 GHz TRX pin of the EFR32FG1 to the
one on-board printed Inverted-F antenna. The component values were optimized for the 2.4 GHz band RF performace and current consumption with 19.5 dBm output power.
For detailed description of the matching network see Chapter 4.2.2 Description of the 2.4 GHz RF Matching.
3.3.6 Inverted-F Antenna
The BRD4251A Radio Board includes a printed Inverted-F antenna (IFA) tuned to have close to 50 Ohm impedance at the 2.4 GHz
band.
For detailed description of the antenna see Chapter 4.6 Inverted-F Antenna.
3.3.7 SMA connector
To be able to perform conducted measurements or mount external antenna for radiated measurements, range tests etc., Silicon Labs
added an SMA connector to the Radio Board. The connector allows an external 50 Ohm cable or antenna to be connected during design verification or testing.
3.3.8 UFL Connector
To be able to perform conducted measurements Silicon Labs added an UFL connector to the Radio Board. The connector allows an
external 50 Ohm cable or antenna to be connected during design verification or testing.
Note: By default the output of the matching network is connected to the printed Inverted-F antenna by a series component. It can be
connected to the UFL connector as well through a series 0 Ohm resistor which is not mounted by default. For conducted measurements
through the UFL connector the series component to the antenna should be removed and the 0 Ohm resistor should be mounted (see
Chapter 4.2 Schematic of the RF Matching Network for further details).
3.3.9 Radio Board Connectors
Two dual-row, 0.05” pitch polarized connectors make up the BRD4251A Radio Board interface to the Wireless Starter Kit Mainboard.
For more information on the pin mapping between the EFR32FG1P133F256GM48 and the Radio Board Connector refer to Chapter
2.2 Radio Board Connector Pin Associations.
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RF Section
4. RF Section
4.1 Introduction
This section gives a short introduction to the RF section of the BRD4251A.
4.2 Schematic of the RF Matching Network
The schematic of the RF section of the BRD4251A Radio Board is shown in the following figure.
2.4 GHz Matching Network
L1
AT1
Path Selection
L2
Inverted-F
Antenna
R1
0R
C1
C2
INVERTED_F
TRX Matching & Filter
U1B
EFR32
RF Crystal
10
X1
38.400 MHz
1
11
GND
Supply Filtering
L102
9
C102
100P
C103
10P
PAVDD
R2
0R
NM
Sub-GHz PA
Power Supply
19
2
C106
220N
C107
10P
L4
RFVDD
L5
13
18
17
15
L3
PAVDD
PAVSS
SUBGRF_IN
SUBGRF_ON
RFVSS
Antenna
Connector
GND
L6
C3
L7
16
14
Discrete Balun
C8
Filter
BAL1
L8
4
1
3
2
P1
L9
L10
C9
4
5
C10
C11
C12
ATB2012-50011
C4
C5
2
3
1
C7
Ground
GND
Test
Connector
U.FL
GND
SUBGRF_OP
SUBGRF_IP
21
3
C14
PA Power
2
P2
1
GND
VBIAS
L103
1
BLM18AG601SN1
GND
VBIAS
20
HFXO
RF Analog Power
2
BLM18AG601SN1
2G4RF_IOP
2G4RF_ION
1
4
VDCDC
RF I/O
HFXI
3
High Frequency
2
Crystal
GND
C6
TRX Matching
C13
SMA
TP1
GND
GND
GND
GND
Sub-GHz Matching Network
Figure 4.1. Schematic of the RF Section of the BRD4251A
The RF matching comprises two separate TX/RX matching networks: one for the sub-GHz RF path, the other for the 2.4 GHz RF path.
4.2.1 Description of the Sub-GHz RF Matching
The sub-GHz matching network connects the differential TX outputs and RX inputs of the sub-GHz RF port to the SMA connector while
transforming the impedances to 50 Ohm. Careful design procedure was followed to ensure that the RX input circuitry does not load
down the TX output path while in TX mode and that the TX output circuitry does not degrade receive performance while in RX mode.
The matching includes a differential impedance matching circuitry, a discrete balanced-unbalanced transformer and a filter section. The
targeted output power is 19.5 dBm at 490 MHz.
4.2.2 Description of the 2.4 GHz RF Matching
The 2.4 GHz matching connects the 2G4RF_IOP pin to the on-board printed Inverted-F Antenna. The 2G4RF_ION pin is connected to
ground. For higher output powers (13 dBm and above) beside the impedance matching circuitry it is recommended to use additional
harmonic filtering as well at the RF output. The targeted output power of the BRD4251A board is 19.5 dBm thus the RF output of the IC
is connected to the antenna through a four-element impedance matching and harmonic filter circuitry.
For conducted measurements the output of the matching network can also be connected to the UFL connector by relocating the series
R1 0 Ohm resistor to the R2 position between the output of the matching and the UFL connector.
4.3 RF Section Power Supply
On the BRD4251A Radio Board the supply pin of the radio (RFVDD) is connected directly ot the output of the on-chip DC-DC converter
while the supply for the sub-GHz and 2.4 GHz power amplifiers (VBIAS) is provided directly by the Motherboard. This way, by default,
the DC-DC converter provides 1.8 V for the RF analog section, the Motherboard provides 3.3 V for the PAs (for details, see the schematic of the BRD4251A).
4.4 Bill of Materials for the sub-GHz Matching
The Bill of Materials of the sub-GHz matching network of the BRD4251A Radio Board is shown in the following table.
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RF Section
Table 4.1. Bill of Materials for the BRD4251A 490 MHz 19.5 dBm RF Matching Network
Component name
Value
Manufacturer
Part Number
BAL1
Balun
TDK Corporation
ATB2012-50011
C3
1.6 pF
Murata
GRM1555C1H1R6WA01
C4
1.6 pF
Murata
GRM1555C1H1R6WA01
C5
Not Mounted
-
-
C6
Not Mounted
-
-
C7
3.3 pF
Murata
GRM1555C1H3R3WA01
C8
220 pF
Murata
GRM1555C1H221GA01
C9
220 pF
Murata
GRM1555C1H221GA01
C10
6.2 pF
Murata
GRM1555C1H6R2BA01
C11
10 pF
Murata
GRM1555C1H100GA01
C12
6.2 pF
Murata
GRM1555C1H6R2BA01
C13
Not Mounted
-
-
C14
220 pF
Murata
GRM1555C1H221GA01
L3
62 nH
Murata
LQW18AN62NG00
L4
470 nH
Murata
LQW18CNR47J00
L5
470 nH
Murata
LQW18CNR47J00
L6
9.1 nH
Murata
LQW15AN9N1G00
L7
9.1 nH
Murata
LQW15AN9N1G00
L8
22 nH
Murata
LQW15AN22NG00
L9
22 nH
Murata
LQW15AN22NG00
L10
0 Ohm
-
-
4.5 Bill of Materials for the 2.4 GHz Matching
The Bill of Materials of the 2.4 GHz matching network of the BRD4251A Radio Board is shown in the following table.
Table 4.2. Bill of Materials for the BRD4251A 2.4 GHz 19.5 dBm RF Matching Network
Component name
Value
Manufacturer
Part Number
C1
2.0 pF
Murata
GRM1555C1H2R0WA01
C2
1.0 pF
Murata
GRM1555C1H1R0WA01
L1
1.8 nH
Murata
LQP15MN1N8W02
L2
3.0 nH
Murata
LQP15MN3N0W02
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RF Section
4.6 Inverted-F Antenna
The BRD4251A Radio Board includes an on-board printed Inverted-F Antenna tuned for the 2.4 GHz band. Due to the design restrictions of the Radio Board the input of the antenna and the output of the matching network can't be placed directly next to each other thus
a 50 Ohm transmission line was necessary to connect them. The resulting impedance and reflection measured at the output of the
matcing network are shown in the following figure. As it can be observed the impedance is close to 50 Ohm (the reflection is better than
-10 dB) for the entire 2.4 GHz band.
Figure 4.2. Impedance and Reflection of the Inverted-F Antenna of the BRD4251A
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Mechanical Details
5. Mechanical Details
The BRD4251A EFR32 Flex Gecko Radio Board is illustrated in the figures below.
2.4 GHz
Matching
DC-DC
Inductor
30 mm
LFXTAL
DC-DC
&
Supply
Filter
Caps.
OTA
Flash
UFL
Connector
RF Output
Selection
EFR32xx
Sub-GHz RF
Matching
and Filter
Frame of
the
Optional
Shielding
Can
Printed
Inverted-F
Antenna
SMA Connector
HFXTAL
4.4 mm
38.6 mm
45 mm
Figure 5.1. BRD4251A Top View
24 mm
5 mm
Display
Enable
Selection
Board
Identification
27.3 mm
PAVDD
Supply
Selection
15 mm
Interface
Connector
28.6 mm
WSTK
Sensor
Enable
Selection
Interface
Connector
Figure 5.2. BRD4251A Bottom View
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EMC Compliance
6. EMC Compliance
6.1 Introduction
Compliance of the fundamental and harmonic levels is tested at the listed frequencies against the listed EMC regulations:
• 490 MHz:
• AMR
• 2.4 GHz:
• ETSI EN 300-328
• FCC 15.247
6.2 EMC Regulations for 490 MHz
6.2.1 AMR Emission Limits for the 470-510 MHz Band
Based on the AMR regulation the allowed maximum fundamental power for the 470-510 MHz band is 50 mW (17 dBm) e.r.p. both for
conducted and radiated measurements.
Note: Further in this document EIRP (Effective Isotropic Radiated Power) will be used instead of e.r.p. (Effective Radiated Power) for
the comparison of the radiated limits and measurement results. The 50 mW e.r.p radiated limit is equivalent to 19.1 dBm EIRP.
For the unwanted emissions AMR specifies the following limits:
• For frequencies between 30 MHz and 1 GHz, the limit is -36 dBm in e.r.p (-33.9 dBm in EIRP).
• For frequencies above 1 GHz, the limit is -30 dBm in e.r.p (-27.9 dBm in EIRP).
6.3 EMC Regulations for 2.4 GHz
6.3.1 ETSI EN 300-328 Emission Limits for the 2400-2483.5 MHz Band
Based on ETSI EN 300-328 the allowed maximum fundamental power for the 2400-2483.5 MHz band is 20 dBm EIRP. For the unwanted emissions in the 1 GHz to 12.75 GHz domain the specified limit is -30 dBm EIRP.
6.3.2 FCC15.247 Emission Limits for the 2400-2483.5 MHz Band
FCC 15.247 allows conducted output power up to 1 Watt (30 dBm) in the 2400-2483.5 MHz band. For spurious emmissions the limit is
-20 dBc based on either conducted or radiated measurement, if the emission is not in a restricted band. The restricted bands are specified in FCC 15.205. In these bands the spurious emission levels must meet the levels set out in FCC 15.209. In the range from
960 MHz to the frequency of the 5th harmonic it is defined as 0.5 mV/m at 3 m distance (equals to -41.2 dBm in EIRP).
Additionally, for spurious frequencies above 1 GHz FCC 15.35 allows duty-cycle relaxation to the regulatory limits. For the EmberZNet
PRO the relaxation is 3.6 dB. So practically the -41.2 dBm limit can be modified to -37.6 dBm.
In case of operating in the 2400-2483.5 MHz band the 2nd, 3rd and 5th harmonics can fall into restricted bands so for those the
-37.6 dBm limit should be applied. For the 4th harmonic the -20 dBc limit should be applied.
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EMC Compliance
6.3.3 Applied Emission Limits for the 2.4 GHz Band
The above ETSI limits are applied both for conducted and radiated measurements.
The FCC restricted band limits are radiated limits only. Besides that, Silicon Labs applies those to the conducted spectrum i.e. it is assumed that in case of a custom board an antenna is used which has 0 dB gain at the fundamental and the harmonic frequencies. In that
theoretical case, based on the conducted measurement, the compliance with the radiated limits can be estimated.
The overall applied limits are shown in the table below.
Table 6.1. Applied Limits for Spurious Emissions for the 2.4 GHz Band
Harmonic
Frequency
Limit
2nd
4800~4967 MHz
-37.6 dBm
3rd
7200~7450.5 MHz
-37.6 dBm
4th
9600~9934 MHz
-30 dBm
5th
12000~12417.5 MHz
-37.6 dBm
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RF Performance
7. RF Performance
7.1 Conducted Power Measurements
During measurements the BRD4251A Radio Board was attached to a Wireless Starter Kit Mainboard which was supplied by USB. The
voltage supply for the Radio Board was 3.3 V.
7.1.1 Conducted Measurements in the 490 MHz band
The BRD4251A Radio Board was connected directly to a Spectrum Analyzer through its SMA connector. The supply for the radio
(RFVDD) was 1.8 V provided by the on-chip DC-DC converter, the supply for the power amplifier (VBIAS) was 3.3 V provided by the
Motherboard (for details, see the schematic of the BRD4251A). The transceiver was operated in continuous carrier transmission mode.
The output power of the radio was set to 19.5 dBm.
The typical output spectrum is shown in the following figure.
Figure 7.1. Typical Output Spectrum of the BRD4251A
As it can be observed the fundamental is a bit higher than 19.5 dBm so it is above the 19.1 dBm fundamental limit thus slight output
power reduction is required to be compliant. The strongest unwanted emission is the double-frequency harmonic but even with
19.5 dBm output power its level is only around -57 dBm.
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RF Performance
7.1.2 Conducted Measurements in the 2.4 GHz band
The BRD4251A Radio Board board was connected directly to a Spectrum Analyzer through its UFL connector (the 0 Ohm resistor was
removed from the R1 position and was soldered to the R2 position). The supply for the radio (RFVDD) was 1.8 V provided by the onchip DC-DC converter, the supply for the power amplifier (VBIAS) was 3.3 V provided by the Motherboard (for details, see the schematic of the BRD4251A). The transceiver was operated in continuous carrier transmission mode. The output power of the radio was set to
19.5 dBm.
The typical output spectrum is shown in the following figure.
Figure 7.2. Typical Output Spectrum of the BRD4251A
As it can be observed the fundamental is slightly lower than 19.5 dBm limit and the strongest unwanted emission is the double-frequency harmonic but with its -44.97 dBm level it is under the -37.6 dBm applied limit with ~7 dB margin. So the conducted spectrum is compliant with the applied limits.
Note: The conducted measurement is performed by connecting the on-board UFL connector to a Spectrum Analyzer through an SMA
Conversion Adapter (P/N: HRMJ-U.FLP(40)). This connection itself introduces approx. 0.3 dB insertion loss.
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RF Performance
7.2 Radiated Power Measurements
During measurements the BRD4251A Radio Board was attached to a Wireless Starter Kit Mainboard which was supplied by USB. The
voltage supply for the Radio Board was 3.3 V. The radiated power was measured in an antenna chamber by rotating the DUT in 360
degree with horizontal and vertical reference antenna polarizations in the XY, XZ and YZ cuts. The measurement axes are as shown in
the figure below.
Figure 7.3. DUT: Radio Board with the Wireless Starter Kit Mainboard (Illustration)
Note: The radiated measurement results presented in this document were recorded in an unlicensed antenna chamber. Also the radiated power levels may change depending on the actual application (PCB size, used antenna etc.) therefore the absolute levels and
margins of the final application is recommended to be verified in a licensed EMC testhouse!
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RF Performance
7.2.1 Radiated Measurements in the 490 MHz band
For the 490 MHz radiated power measurements an external whip antenna (P/N: EXC470SM (Laird Technologies)) was used as a transmitter antenna. It was connected to the SMA connector of the BRD4251A Radio Board. The supply for the radio (RFVDD) was 1.8 V
provided by the on-chip DC-DC converter, the supply for the power amplifier (VBIAS) was 3.3 V provided by the Motherboard (for details, see the schematic of the BRD4251A). The transceiver was operated in continuous carrier transmission mode. The output power of
the radio was set to 19.5 dBm.
The measured radiated powers are shown in the table below.
Table 7.1. Maximums of the Measured Radiated Powers of BRD4251A at 490 MHz
490 MHz
EIRP [dBm]
Orientation
Margin [dB]
Limit in EIRP [dBm]
Fundamental
19.9
XY/V
-0.8
19.1
2nd harmonic
-44.5
YZ/H
10.6
-27.9
3rd harmonic
-46.8
XZ/H
18.9
-27.9
4th harmonic
-31.3
YZ/H
3.4
-27.9
5th harmonic
-52.9
XZ/H
25.0
-27.9
6th harmonic
-45.1
XZ/H
17.2
-27.9
7th harmonic
-51.4
XZ/V
23.5
-27.9
8th harmonic
-37.0
XZ/H
9.1
-27.9
9th harmonic
-55.5
YZ/H
27.6
-27.9
10th harmonic
-51.0
XZ/H
23.1
-27.9
* Signal level is below the Spectrum Analyzer noise floor.
As it can be observed the fundamental is sligthly above the regulation limit so the reduction of the output power is required to comply.
The harmonic levels are compliant even with 19.5 dBm output power.
7.2.2 Radiated Measurements in the 2.4 GHz band
For the 2.4 GHz radiated power measurements the on-board printed Inverted-F antenna of the BRD4251A Radio Board was used (the
R1 resistor was mounted). The supply for the radio (RFVDD) was 1.8 V provided by the on-chip DC-DC converter, the supply for the
power amplifier (VBIAS) was 3.3 V provided by the Motherboard (for details, see the schematic of the BRD4251A). The transceiver was
operated in continuous carrier transmission mode. The output power of the radio was set to 19.5 dBm. During the measurement the
sub-GHz antenna (P/N: EXC470SM (Laird Technologies)) was attached to the SMA connector.
The results are shown in the table below.
Table 7.2. Maximums of the Measured Radiated Powers of BRD4251A at 2.4 GHz
2.4 GHz
EIRP [dBm]
Orientation
Margin [dB]
Limit in EIRP [dBm]
Fundamental
21.6
XY/H
8.4
30
2nd harmonic
-41.3
YZ/V
3.7
-37.6
3rd harmonic
<-50*
-/-
>10
-37.6
4th harmonic
<-50*
-
>30
-30
5th harmonic
<-50*
-
>10
-37.6
* Signal level is below the Spectrum Analyzer noise floor.
As it can be observed, thanks to the ~2-3 dB gain of the on-board Inverted-F antenna, the level of the fundamental is higher than
19.5 dBm. The harmonic levels are comliant with the applied limits with large margins.
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BRD4251A Reference Manual
EMC Compliance Recommendations
8. EMC Compliance Recommendations
8.1 Recommendations for 490 MHz AMR compliance
As it was shown in the previous chapter both the conducted and the radiated power of the fundamental of the BRD4251A EFR32 Flex
Gecko Radio Board slightly exceeds the 19.1 dBm limit of the AMR regulation with 19.5 dBm output power so reduction of the fundamental power is required by approx. 1 dB in order to comply. Although the BRD4251A Radio Board has an option for mounting a shielding can, that is not required for the compliance.
8.2 Recommendations for 2.4 GHz ETSI EN 300-328 compliance
As it was shown in the previous chapter the radiated power of the fundamental of the BRD4251A EFR32 Flex Gecko Radio Board with
19.5 dBm output power exceeds the 20 dBm limit of the ETSI EN 300-328 regulation due to the high antenna gain so reduction of the
fundamental power is required by approx. 2 dB in order to comply. The harmonic emissions are under the -30 dBm limit with large margin even with 19.5 dBm output power. Although the BRD4251A Radio Board has an option for mounting a shielding can, that is not
required for the compliance.
8.3 Recommendations for 2.4 GHz FCC 15.247 compliance
As it was shown in the previous chapter the BRD4251A EFR32 Flex Gecko Radio Board is compliant with the emission limits of the
FCC 15.247 regulation with 19.5 dBm output power. Although the BRD4251A Radio Board has an option for mounting a shielding can,
that is not required for the compliance.
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Rev. 1.00 | 15
BRD4251A Reference Manual
Document Revision History
9. Document Revision History
Table 9.1. Document Revision History
Revision Number
Effective Date
Change Description
1.0
20.05.2016
Initial release.
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Rev. 1.00 | 16
BRD4251A Reference Manual
Board Revisions
10. Board Revisions
Table 10.1. BRD4251A Radio Board Revisions
Radio Board Revision
Description
A00
Initial release.
B00
Changing board design to support dual-band operation (490 MHz/2.4 GHz). Updating sub-GHz matching
network.
B01
Sub-GHz PA supplied from VBIAS (filtered PAVDD).
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Rev. 1.00 | 17
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Radio Board Connector . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1 Introduction.
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. 2
2.2 Radio Board Connector Pin Associations.
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3. Radio Board Block Summary . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1 Introduction.
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3.2 Radio Board Block Diagram .
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3.3 Radio Board Block Description .
3.3.1 Wireless MCU . . . . . .
3.3.2 LF Crystal Oscillator (LFXO) .
3.3.3 HF Crystal Oscillator (HFXO) .
3.3.4 Matching Network for Sub-GHz
3.3.5 Matching Network for 2.4 GHz.
3.3.6 Inverted-F Antenna . . . .
3.3.7 SMA connector . . . . . .
3.3.8 UFL Connector . . . . . .
3.3.9 Radio Board Connectors . .
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4. RF Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1 Introduction.
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4.2 Schematic of the RF Matching Network . .
4.2.1 Description of the Sub-GHz RF Matching .
4.2.2 Description of the 2.4 GHz RF Matching .
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4.3 RF Section Power Supply .
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4.4 Bill of Materials for the sub-GHz Matching .
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4.5 Bill of Materials for the 2.4 GHz Matching
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4.6 Inverted-F Antenna .
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5. Mechanical Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. EMC Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1 Introduction.
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. 9
6.2 EMC Regulations for 490 MHz . . . . . . .
6.2.1 AMR Emission Limits for the 470-510 MHz Band
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6.3 EMC Regulations for 2.4 GHz . . . . . . . . . . . . .
6.3.1 ETSI EN 300-328 Emission Limits for the 2400-2483.5 MHz Band
6.3.2 FCC15.247 Emission Limits for the 2400-2483.5 MHz Band. . .
6.3.3 Applied Emission Limits for the 2.4 GHz Band . . . . . . .
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.10
7. RF Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
7.1 Conducted Power Measurements . . . . . .
7.1.1 Conducted Measurements in the 490 MHz band
7.1.2 Conducted Measurements in the 2.4 GHz band .
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.11
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.12
Table of Contents
18
7.2 Radiated Power Measurements . . . . . . .
7.2.1 Radiated Measurements in the 490 MHz band .
7.2.2 Radiated Measurements in the 2.4 GHz band .
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8. EMC Compliance Recommendations . . . . . . . . . . . . . . . . . . . . .
15
8.1 Recommendations for 490 MHz AMR compliance .
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8.2 Recommendations for 2.4 GHz ETSI EN 300-328 compliance
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.15
8.3 Recommendations for 2.4 GHz FCC 15.247 compliance
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.15
9. Document Revision History . . . . . . . . . . . . . . . . . . . . . . . . .
16
10. Board Revisions. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
Table of Contents
19
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